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搜狗的一道关于加密解密的笔试题,很有意思!
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这是一道搜狗的笔试题,要求在30分钟内完成。

根据下面的 encode 方法写出对应的 decode 方法。最后运行程序输出的结果就是要求的答案。

先不看答案,trying一下吧。程序如下:

public class Test { 

    public static void encode(byte[] in, byte[] out, int password) { 
        int len = in.length; 

        int seed = password ^ 0x8c357ca5; 
        for (int i = 0; i < len; ++i) { 
            byte a = (byte) ((in[i] ^ seed) >>> 5); 
            byte b = (byte) (((((int) in[i]) << 16) ^ seed) >>> (16 - 3)); 
            a &= 0x7; 
            b &= 0xf8; 
            out[i] = (byte) (a | b); 
            seed = (seed * 3687989 ^ seed ^ in[i]); 
        } 
    } 

    public static void decode(byte[] in, byte[] out, int password) { 
        int len = in.length; 

        int seed = password ^ 0x8c357ca5; 
        for (int i = 0; i < len; ++i) { 
            // fill the code here 
        } 
    } 

    public static void main(String[] args) throws Exception { 
        int password = 0xe87dd9d3; 
        byte[] buf1 = { 29, -16, 96, 43, -85, 25, -96, 83, 13, 66, -109, 49, -111, 0, 60, -101, 99, -86, -38, 86, -35, 
                48, 23, 83, -102, 25, 73, -116, -101, -88, -5, 14, -14, -112, 87, -87, 2, 108, -58, 40, 56, 12, 108, 
                77, 83, 38, 20, -114, }; 
        byte[] buf2 = new byte[buf1.length]; 
        decode(buf1, buf2, password); 
        System.out.println(new String(buf2, "GBK")); 
    } 
} 

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最后输出结果是:搜狗输入法支持各种炫酷的皮肤,彰显个性的你!!!
其中一种实现方式为:

byte a = (byte) (((in[i]&0x7) <<5) ^seed); 
byte b = (byte) ((((((int) in[i])&0xf8) << 13) ^ seed) >>> 16); 
a &= 0xe0; 
b &= 0x1f; 
out[i] = (byte) (a | b); 
seed = (seed * 3687989 ^ seed ^ out[i]);
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发帖于7年前 6回/1K+阅
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